The earliest aquarium dates from 1882 and was located in the Zoo of Ueno - unfortunately, that aquarium is no more.
The oldest one still in existence (and now much enlarged and refurbished) is the Matsushima Aquarium Marinepia near Sendai, which was established in 1927.
[The glass dome of Tokyo Sea Life Park]
The three largest aquariums in Japan are the Osaka Kaiyukan Aquarium, the Toba Aquarium near Ise, and the Tokyo Sea Life Park Aquarium.
The Osaka Kaiyukan is one of the largest aquariums in the world and (based on the "Gaia Hypothesis" by Lovelock) recreates the Pacific Rim volcanic belt and the Pacific Rim life belt. The Toba Aquarium boasts many larger sea creatures as dugongs, otters and porpoise - and besides that 40,000 sea creatures in 700 species, too much to see even in a whole day.
The Tokyo Sea Life Park stands at Tokyo Bay (near Disneyland) and - besides being housed in a beautiful piece of architecture by Taniguchi Yoshio - is famous for its donut-shaped tank where bluefin tunas swim around in endless motion.
Besides that, there are numerous regional aquariums that all have their own specialisms.
The Lake Biwa Museum is dedicated to Japan's largest sweet water collection, and the Chitose Salmon Aquarium specializes in salmon and fresh-water fish of the northern Pacific (and has an observation room built into the river where one can see the live fish through glass).
[Tuna fish in the tank of Tokyo Sea Life Park]
Some aquariums have a special technical prowess, such as the Shimoda Aquarium, which has fish unique to the Izu Peninsula and offers divers the opportunity to swim with dolphins (for a fee). It was also the first aquarium in Japan to be built in the water - it floats on the sea.
The big tank of the Kushimoto Marine Park in Wakayama has a glass roof and faithfully recreates the sealife of the area.
If you don't have either if these qualities, you have to be cunning in the battle for customers.
The Enoshima Aquarium therefore puts on shows of dancing jellyfish where people can go for stress relief.